Overlay measuring apparatus

ABSTRACT

The present application provides an overlay measuring apparatus, adapted to determine relative positions of two or more successive patterned layers of a device. The overlay measuring apparatus includes a stage and an imaging assembly. The device is placed on the stage. The imaging assembly includes a plurality of optical heads and a plurality of overlay marks assembled on the optical heads. The relative positions of the two or more successive patterned layers of the device are determined using light reflected from the device and passing through the overlay mark mounted on the respective optical head.

TECHNICAL FIELD

The present disclosure relates to an overlay measurement technique,which is used in semiconductor manufacturing processes, and moreparticularly, to an overlay mark for measuring an alignment errorbetween different layers, or between different patterns on a same layer,of a semiconductor wafer stack.

DISCUSSION OF THE BACKGROUND

Semiconductor devices such as memory devices are typically fabricated bya sequence of processing steps applied to a specimen. Various featuresand multiple structural levels of the semiconductor devices are formedby such processing steps. For example, lithography, among others, is onesemiconductor fabrication process that involves generating a pattern ona semiconductor wafer. Additional examples of semiconductor fabricationprocesses include, but are not limited to, ion implantation (doping),deposition, etching, metallization, oxidation, and chemical-mechanicalpolishing. Multiple semiconductor devices may be fabricated on a singlesemiconductor wafer and then separated into individual semiconductordevices by a technique such as dicing or sawing.

Semiconductor devices are often fabricated by depositing a series oflayers on a substrate. Some or all of the layers include variouspatterned structures. Relative positions of the structures both within alayer and between layers is critical to performance of completedelectronic devices. Overlay refers to the relative position of overlyingor interlaced structures on a same or different layers of a wafer.Overlay error refers to deviations from a nominal relative position ofoverlying or interlaced structures. A greater overlay error leads togreater misalignment of the structures. If the overlay error is toogreat, the performance of the manufactured electronic device may becompromised.

Image-based overlay (IBO) measurement is a very common technique used inintegrated circuit manufacturing to extract overlay error values. Theoverlay error is measured using dedicated overlay targets, which areoptimized to increase accuracy and resolution of the overlay. However,the dedicated overlay targets are much larger than product features ofthe integrated circuit. The IBO measurement is based on the dedicatedtargets instead of on the product features, because the current overlaymetrology solutions, mainly based on optics, cannot provide sufficientresolution using the product features.

This Discussion of the Background section is provided for backgroundinformation only. The statements in this Discussion of the Backgroundare not an admission that the subject matter disclosed in thisDiscussion of the Background section constitute prior art to the presentdisclosure, and no part of this Discussion of the Background section maybe used as an admission that any part of this application, includingthis Discussion of the Background section, constitutes prior art to thepresent disclosure.

SUMMARY

One aspect of the present disclosure provides an overlay measuringapparatus for determining relative positions of two or more successivepatterned layers of a device. The overlay measuring apparatus includes astage and an imaging assembly configured to record images of the deviceplaced on the stage. The imaging assembly includes a plurality ofoptical heads configured to capture the images of the device and aplurality of overlay marks assembled on the plurality of optical heads,respectively. The relative positions of the two or more successivepatterned layers of the device are determined using light reflected fromthe device and passing through the respective overlay mark mounted onthe optical head.

In some embodiments, the overlay measuring apparatus further includes acomputer configured to execute algorithms that calculate a relativedisplacement between the successive patterned layers using electricalsignals transferred from the image captured by the optical head.

In some embodiments, the computer analyzes a difference between apredetermined intensity distribution of light reflected by the deviceand a unique intensity distribution of the light reflected by the deviceand passing through the respective overlay mark to obtain the relativedisplacement of the patterned layers of the device.

In some embodiments, the computer is configured to control a movement ofthe stage, and is further configured to select the optical head torecord the image.

In some embodiments, the imaging assembly further includes a lightsource configured to generate light to illuminate the device.

In some embodiments, the imaging assembly further includes a beamsplitter disposed at an intersection of axes of the light source and theoptical head, wherein the beam splitter reflects the light generatedfrom the light source, and the light reflected from the device passesthrough the beam splitter and the respective overlay mark and isincident on the respective optical head.

In some embodiments, the overlay measuring apparatus further includes afirst lens and a second lens, wherein the first lens is disposed betweenthe beam splitter and the device, and the second lens is disposedbetween the beam splitter and the optical head.

In some embodiments, the overlay mark comprises a plurality ofmicro-structures arranged in a concentric configuration.

In some embodiments, the micro-structures include circles.

In some embodiments, the micro-structures include squares.

In some embodiments, the micro-structures further include two linesintersecting at a center of the squares and dividing the squares intoquarters.

In some embodiments, the micro-structures include rhombuses.

In some embodiments, the micro-structures further comprise four linesextending outward from centers of sides of an outmost one of therhombuses.

In some embodiments, the micro-structures further include a plurality oflines spaced apart from an outermost one of the rhombuses with a firstpitch greater than a second pitch between two of the rhombuses adjacentto each other.

In some embodiments, the overlay mark is composed of repetitiousmicro-structures.

In some embodiments, the overlay mark is a rhombus and is composed of aplurality of rhomboidal micro-structures.

In some embodiments, the micro-structures are rectangular and arearranged in a running bond configuration.

In some embodiments, the overlay mark includes rhomboidal or hexagonalmicro-structures.

In some embodiments, the micro-structures have a gammadion shape.

In some embodiments, the overlay mark includes a plurality oftrapezoidal micro-structures and a plurality of inverted trapezoidalmicro-structures alternately interlaced with each other.

In some embodiments, the overlay mark includes zigzag micro-structures.

In some embodiments, the overlay mark comprises multiple overlappingsquare micro-structures, and each of the overlapping squaremicro-structures is composed of four small squares.

In some embodiments, the overlay measuring apparatus further includes apassivation film covering the plurality of overlay marks.

One aspect of the present disclosure provides an optical system. Theoptical system comprises a device and an overlay measuring apparatus.The device includes a first patterned layer, a second patterned layerand a first passivation film. The second patterned layer is disposedabove the first patterned layer, and the first passivation film coversthe first patterned layer. The overlay measuring apparatus fordetermining relative position of first and second patterned layersincludes a stage and an imaging assembly. The device is placed on thestage. The imaging assembly comprises a plurality of optical heads and aplurality of overlay marks. The plurality of optical heads areconfigured to record at least one image of the device. The plurality ofoverlay marks are assembled on the plurality of optical heads,respectively. The relative position of the first and second patternedlayers are determined using light reflected from the device and passingthrough the respective overlay mark mounted on the optical head.

In some embodiments, the device further includes a second passivationfilm covering the second patterned layer.

In some embodiments, the device further includes at least onesemiconductor layer disposed between the first passivation film and thesecond patterned layer, and the second patterned layer is configured topattern the semiconductor layer during etching.

In some embodiments, the overlay measuring apparatus further includes acomputer configured to execute algorithms that calculate a relativedisplacement of the first and second patterned layers using electricalsignals transferred from the image recorded by the optical head.

In some embodiments, wherein the overlay mark comprises a plurality ofmicro-structures arranged in a concentric configuration.

In some embodiments, the overlay mark is composed of repetitiousmicro-structures.

One aspect of the present disclosure provides a method of operating anoverlay measuring apparatus. The method includes steps of providing aplurality of optical heads; assembling a plurality of overlay marks onthe plurality of optical heads; placing a device to be measured on astage; aligning one of the plurality of optical heads with the device;and recording at least one image of the device.

In some embodiments, the method further includes a step of calculating arelative displacement of patterns on the device based on the at leastone image.

In some embodiments, the calculation is performed by a computerelectrically coupled to the imaging assembly.

In some embodiments, the computer is electrically coupled to the stageto control a movement of the stage.

In some embodiments, the method further includes a step of providing alight source to illuminate the device.

In some embodiments, the method further includes providing a beamsplitter and positioning the beam splitter at an intersection of opticalaxes of the light source and the optical head for recording the image ofthe device.

In some embodiments, the overlay mark comprises a periodic structure.

With the above-mentioned configurations of the overlay measuringapparatus, the test pattern of the overlay mark is mounted on theoptical head and is replaceable during the measurement; therefore, therecorded image may have a better resolution, and thus an accuracy of themeasurement is improved.

The foregoing has outlined rather broadly the features and technicaladvantages of the present disclosure in order that the detaileddescription of the disclosure that follows may be better understood.Additional features and technical advantages of the disclosure aredescribed hereinafter, and form the subject of the claims of thedisclosure. It should be appreciated by those skilled in the art thatthe concepts and specific embodiments disclosed may be utilized as abasis for modifying or designing other structures, or processes, forcarrying out the purposes of the present disclosure. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit or scope of the disclosure as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure may be derivedby referring to the detailed description and claims. The disclosureshould also be understood to be coupled to the figures' referencenumbers, which refer to similar elements throughout the description.

FIG. 1 is a schematic view of an optical system in accordance with someembodiments of the present disclosure.

FIG. 2 is a cross-sectional view of a device in accordance with someembodiments of the present disclosure.

FIGS. 3 to 18 illustrate overlay marks used to determine the alignmentof two layers of a semiconductor wafer in accordance with someembodiments of the present disclosure.

FIG. 19 is a schematic view of an optical system in accordance with someembodiments of the present disclosure.

FIG. 20 is a cross-sectional view of a device in accordance with someembodiments of the present disclosure.

FIG. 21 is a schematic view of an optical system in accordance with someembodiments of the present disclosure.

FIG. 22 is a flow diagram illustrating a method of operating overlaymeasuring apparatus in accordance with some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

Embodiments, or examples, of the disclosure illustrated in the drawingsare described below using specific language. It shall be understood thatno limitation of the scope of the disclosure is hereby intended. Anyalteration or modification of the described embodiments, and any furtherapplications of principles described in this document, are to beconsidered as normally occurring to one of ordinary skill in the art towhich the disclosure relates. Reference numerals may be repeatedthroughout the embodiments, but this does not necessarily mean thatfeature(s) of one embodiment apply to another embodiment, even if theyshare the same reference numeral.

It shall be understood that, although the terms first, second, third,etc. may be used herein to describe various elements, components,regions, layers or sections, these elements, components, regions, layersor sections are not limited by these terms. Rather, these terms aremerely used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of the present inventive concept.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting to thepresent inventive concept. As used herein, the singular forms “a,” “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It shall be understood that theterms “comprises” and “comprising,” when used in this specification,point out the presence of stated features, integers, steps, operations,elements, or components, but do not preclude the presence or addition ofone or more other features, integers, steps, operations, elements,components, or groups thereof.

FIG. 1 is a schematic view of an optical system 10 in accordance withsome embodiments of the present disclosure. Referring to FIG. 1 , theoptical system 10 includes an overlay measuring apparatus 20 and adevice 30. The overlay measuring apparatus 20 is used to provideinformation of overlay between different layers or between differentpatterns on a same layer of the device 30. More particularly, theoverlay measuring apparatus 20 is used in semiconductor manufacturingprocesses and used to determine how accurately a first patterned layer310 (as shown in FIG. 2 ) of the device 30 aligns with a secondpatterned layer 320 disposed above or below the first patterned layer310. Alternatively, the overlay measuring apparatus 20 may be employedto determine how accurately a first pattern on the device 30 aligns witha second pattern on the device 30 disposed on the same layer. The device30 may include various elements, such as semiconductor components,bipolar junction transistor, resistors, capacitors, diodes, fuses, etc.,but is simplified for a better understanding of the concepts of thepresent disclosure.

Referring to FIGS. 1 and 2 , the overlay measuring apparatus 20,configured to determine a relative shift between the first and secondpatterned layers 310 and 320 of the device 30, mainly includes a stage110 capable of horizontal motion and vertical motion and an imagingassembly 120 used to record images of the device 30 placed on the stage110. In some embodiments, the stage 110 is movable in either Cartesiancoordinates or polar coordinates.

The imaging assembly 120 includes a plurality of optical heads 122employed to capture the images of the device 30 for integrated circuitsand a plurality of overlay marks 124 assembled on the optical heads 122.The overlay marks 124, mounted on the optical heads 122, have testpatterns. Notably, the overlay marks 124, used to monitor overlaydeviation between the first and second patterned layers 310 and 320 ofthe device 30, are optically transparent and allow light to pass throughwithout appreciable scattering of the light.

The optical head 122, right above the device 30, can receive lightreflecting off the device 30 and passing through the respective overlaymark 124, and can transform the light with a unique intensitydistribution into corresponding electrical signals, which are sent to acomputer 100 and which can be used by the computer 100. In someembodiments, the computer 100 includes a standardized operation systemcapable of running general-purpose application software for assistingwith analysis of process performance data and for communicating with thestage 110 and the optical head 122 via communication ports thereof. Thecomputer 100 may monitor the status of the imaging assembly 120, andthen provide instructions to the imaging assembly 120 based on themonitoring results.

After receiving the electrical signals, the computer 100 executesanalysis algorithms that calculate a relative displacement of the firstand second patterned layers 310 and 320 of the device 30 based on thecaptured image(s). Information associated with conditions measured bythe optical head 122 is transmitted to the computer 100, which executesreal-time and/or post-measurement analysis to predict a quality of thedevice 30.

Generally, the light reflected by the device 30 has a predeterminedintensity distribution, and the light reflecting by the device 30 andpassing through the test patterns of the overlay mark 124 has the uniqueintensity distribution; the computer 100 may analyze the differencebetween the predetermined intensity distribution and the uniqueintensity distribution to obtain the relative displacement of the firstand second patterned layers 310 and 320 of the device 30. In someembodiments, the predetermined intensity distribution may be computed orsimulated from a parameterized mathematical model. Alternatively, ifoverlay marks 124 are detachable, the optical head 122 where the overlaymark 124 is not assembled can receive light directly reflecting off thedevice 30, and can transform the light with the predetermined intensitydistribution into corresponding electrical signals. The electricalsignals are sent to the computer 100 and can be used by the computer100.

The computer 100 is, for example, a workstation, a personal computer ora central processing unit. In some embodiments, the computer 100 is notonly electrically coupled to the optical head 122, but also electricallyconnected to the stage 110 for controlling the movement of the stage 110that holds the device 30. In some embodiments, the computer 100 may beconfigured to track and store the data related to the recorded image(s)and operations of the stage 110 and the optical heads 122 in a computerreadable media. Some common forms of the computer readable media used inthe present disclosure may include, for example, floppy disk, flexibledisk, hard disk, magnetic tape, any other magnetic medium, compact discread-only memory (CD-ROM), any other optical medium, punch cards, papertape, any other physical medium with patterns of holes, random accessmemory (RAM), programmable read-only memory (PROM), erasableprogrammable read-only memory (EPROM), flash-EPROM, any other memorychip or cartridge, carrier wave, or any other medium from which acomputer is adapted to read.

The test patterns of the overlay marks 124 can include a periodicstructure. The test patterns may be composed of a plurality ofmicro-structures, which increases an amount of information that may beused to measure overlay errors, and which may be widely modified todiminish the impact of certain processes on the overlay measurement. Insome embodiments, the micro-structures are about the same size and pitchas structures of actual integrated circuits. By forming each of periodicstructures with micro-structures that are sized closer to the size ofthe actual circuit, a more accurate measurement of any alignment errorin such circuit is obtained. The overlay marks 124 may havemicro-structures arranged in a concentric configuration, as shown inFIGS. 3 to 9 . In alternative embodiments, the overlay marks 124 may becomposed of repetitious micro-structures, as shown in FIGS. 10 to 18 .

Referring to FIGS. 3 to 5 , the micro-structures on the overlay mark 124are concentric circles, concentric squares, or concentric rhombuses. Theoverlay mark 124 in FIGS. 6 and 7 includes multiple concentric squaresand two lines intersecting at a center of the concentric squares anddividing the concentric squares into quarters; the lines in FIG. 6 crosssides of the squares, while the lines in FIG. 7 are diagonals.

Referring to FIGS. 8 to 9 , the micro-structures of the overlay mark 124include a plurality of concentric rhombuses and a plurality of lines. Indetail, the micro-structures in FIG. 8 further include four linesextending outward from centers of sides of outermost rhombuses. In FIG.9 , the micro-structures further include a plurality of lines spacedapart from the outermost rhombuses in a first pitch P1 greater than asecond pitch P2 between the concentric rhombuses; the lines are parallelto sides of the concentric rhombuses.

Referring to FIG. 10 , the overlay mark 124 is a rhombus and is composedof a plurality of rhomboidal micro-structures. The overlay mark 124shown in FIG. 11 includes rectangular micro-structures arranged in arunning bond configuration. Referring to FIGS. 12 and 13 , the overlaymarks 124 are composed of repetitive rhomboidal and hexagonalmicro-structures, respectively.

In FIG. 14 , the overlay mark 124 includes trapezoidal and invertedtrapezoidal micro-structures interlaced with each other. In FIG. 15 ,the overlay mark 124 includes a plurality of circular micro-structuresspaced apart from each other. In FIG. 16 , the overlay mark 124 includeszigzag micro-structures. In FIG. 17 , the overlay mark 124 includesmultiple micro-structures of gammadion (fylfot or swastika) shape. Insome embodiments, the gammadion shape is in a right-hand direction. InFIG. 18 , the overlay mark 124 includes multiple overlapping squaremicro-structures composed of four small squares. The overlay marks 124of the present disclosure are not limited to the above-mentionedembodiments, and may have other different embodiments.

Referring again to FIG. 2 , the device 30 may further include a firstpassivation film 330 disposed between the first patterned layer 310 andthe second patterned layer 320. The first passivation film 330, coveringthe first patterned layer 310, may provide structural strength to thefirst patterned layer 310, which may need to accommodate compressionforces (such as from deposition and/or plating process) and/or shearforce (such as from chemical mechanical polishing process). The firstpassivation film 330 is a conformal layer having a substantially uniformthickness. The first passivation film 330 may be formed on the firstpatterned layer 310 using a plating process or vapor depositionprocesses, such as a chemical vapor deposition (CVD) process or aphysical vapor deposition (PVD) process prior to the deposition of thesecond patterned layer 320. In some embodiments, the first passivationfilm 330 is, for example, a diamond-like carbon (DLC) film or ananocomposite film.

In some embodiments, the device 30 may further includes one or moresemiconductor layers 350 a and 350 b disposed between the firstpassivation film 330 and the second patterned layer 320, wherein thefirst passivation film 330 is formed to cover the first patterned layer310 prior to the deposition of the semiconductor layers 350 a and 350 b.The semiconductor layers 350 a and 350 b are optically transparent, thusallowing the light reflected by the first patterned film 310 to betransmitted through the semiconductor layers 350 a and 350 b andincident onto the optical head 122.

The optical heads 122 are designed with a proper mechanism toeffectively capture light reflected off the device 30. In someembodiments, on-site technicians may charge the overlay marks 124 formeasuring the device 30 by mechanically revolving the optical heads 122.Alternatively, the computer 100 may control the revolving of the opticalheads 122, and thus the test patterns of the overlay mark 124, formeasuring overlay error. By way of example, the optical heads 122 may becharge couple devices (CCDs) or complementary metal-oxide-semiconductor(CMOS) sensors. After the measurement, if the recorded images providedby the optical head 122 do not meet expectations, the on-sitetechnicians may charge the overlay marks 124 and then perform anothermeasurement.

Process conditions such as shadowing and light wavelength can alsoinfluence signal quality. Therefore, the imaging assembly 120 furtherinclude a light source 130 adapted to emit light to illuminate thedevice 30. The light source 130 provides light incident on the device 30to optimize image resolution and to minimize optical aberrations. Thelight source 130 may be configured to provide illumination of a uniformintensity. The light source 130 can provide light at selectivewavelengths, including incoherent or coherent wavelengths. The light forilluminating the device 30 may be generated by electromagneticradiation, such as laser, light-emitting diode (LED), or broadbandradiation. Alternatively, the light may be generated by a bulb. In someembodiments, the light source 130 may be a tunable light source operableto generate light beams with different wavelength to achievemulti-wavelength overlay measurement. Additionally, the light source 130may generate visible light or invisible light including infrared light,near-infrared (NIR) light or far-infrared (FIR) light.

The overlay measuring apparatus 20 can further include a display 102 fordisplaying data related to performance and operation of the overlaymeasuring apparatus 20 to the on-site technicians. The display 102 isfurther configured to accept input data from the on-site technicians. Inother words, the display 102 is provided with a communications linkdirectly to the computer 100 to provide real-time control functions ofthe overlay measuring apparatus 20 by the on-site technicians,particularly where the on-site technicians' intervention is required.

The overlay measuring apparatus 20 can further include operationinterface communication links among the computer 100, the stage 110, theoptical heads 124, the light source 130 and other peripheral devices,and a program sequence of operation which renders the operationinterface capable of monitoring diagnostic functions of the computer100, the stage 110, the optical heads 124, and the light source 130;triggering of sound and/or light alarms regarding conditions of theoptical heads 124 and the light source 130; receiving of performancedata from the optical heads 124; and receiving of input data from one ormore input device including the display 102 and a keyboard. The display102 is also configured to display a measurement result of the overlaymeasuring apparatus 20 to be visualizable to the on-site technicians.

In FIG. 1 , the light generated by the light source 130 travels straightalong a horizontal direction and does not illuminate the device 30;therefore, a beam splitter 132 capable of directing the light is used todirect the light toward the device 30. The beam splitter 132 can bepositioned at an intersection of an optical axis A1 of the light source130 and an optical axis A2 of one of the optical heads 122 that recordsthe image of the device 30. By the use of the beam splitter 132, thelight output from the light source 130 is reflected by the beam splitter132 and its transmission path is directed toward the device 30; thelight reflected off the device 30 may pass through the beam splitter 132and be transmitted to one of the optical heads 122 that records theimage of the device 30. In FIG. 1 , the beam splitter 132 is of a cubeconfiguration; however, the beam splitter 132 may have a plate orpellicle configuration.

The imaging assembly 120 can also include a first lens 134 and a secondlens 136; the first lens 134 is disposed between the beam splitter 132and the device 30, and the second lens 136 is disposed between the beamsplitter 132 and the optical heads 122. The light reflected by the beamsplitter 132 is focused onto the device 30 by the first lens 134, whilethe light passing through the beam splitter 132 is focused onto theoptical head 122 by the second lens 136.

FIG. 19 is a schematic view of an optical system 10 in accordance withsome embodiments of the present disclosure. Referring to FIG. 19 , theoptical system 10 includes an overlay measuring apparatus 20 and adevice 30. The overlay measuring apparatus 20 is used in semiconductormanufacturing processes and used to determine an overlay error of thedevice 30. The overlay measuring apparatus 20 includes a computer 100, astage 110 and an imaging assembly 120; the computer 100 is associatedwith the stage 110 and the imaging assembly 120 and is configured todetermine whether the overlay error exists or not.

FIG. 20 is a cross-sectional view of the device 30 in accordance withsome embodiments of the present disclosure. Referring to FIG. 20 , thedevice 30 includes a first patterned layer 310, a second patterned layer320 disposed above the first patterned layer 310, a first passivationfilm 330 between the first and second patterned layer 310 and 320, and asecond passivation film 340 covering the second patterned layer 320. Thefirst and second passivation films 330 and 340 can provide structuralstrength to the first and second patterned layers 310 and 320,respectively. In some embodiments, the first and second passivationfilms 330 and 240 are DLC films or nanocomposite films.

The second patterned layer 320 may include photoresist material and isformed using a lithography process. The second patterned layer 320 maybe a pattern, which is used to protect portions of the semiconductorlayer 350 b during etching. Commonly, overlay errors are checked afteran exposure operation. In General, the device having unacceptableoverlay error for that particular manufacturing step is reworked byremoving and re-depositing the photoresist layer and re-exposed. In someembodiments, the computer 100 may perform data analysis and calculatethe overlay error, and then provide various instructions to the on-sitetechnicians via network, such as instructions for adjusting layerformation conditions, or instructions for adjusting lithographyconditions in order to eliminate or reduce the overlay error. In someembodiments, the computer 100 may sent instructions to the stage 100 totune the device 30 tilting, rotating, shifting to reduce the overlayerror.

The imaging assembly 120 is used to capture images of the device 30. Thedevice 30 comprises the first and second patterned layer 310 and 320being measured is placed on the stage 110, which is typically motordriven under control of the computer 100. The computer 100 also performsactual calculations based on data received from the imaging assembly120. In some embodiments, the computer 100 includes a standardizedoperation system capable of running general-purpose application softwarefor assisting with the analysis of process performance data and forcommunicating with the stage 110 and the imaging assembly 120 viacommunication ports thereof.

The imaging assembly 120 includes a plurality of optical heads 122 and aplurality of overlay marks 124; the optical heads 122 are employed tocapture images of the device 30, and the overlay marks 124 are assembledon the optical heads 122. Each of the overlay marks 124 is mounted onthe optical heads 122, is optically transparent, and includes a testpattern. The overlay marks 124 may be utilized to measure the alignmentof the first patterned layer 310 of the device 30 with respect to thesecond patterned layer 320 thereof. Additionally, the overlay mark 124may be utilized to measure the alignment of a first pattern of thedevice 30 with respect to a second pattern thereof, wherein the firstpattern and the second pattern are successive patterns formed on thesame semiconductor layer.

The optical head 122 can receive light that is directed to the device30, reflects off the device 30 and passes through the test pattern ofthe respective overlay mark 124. The optical head 122 then transformsthe received light with predetermined intensity distribution intocorresponding electrical signals, and transmits the electrical signalsto the computer 100. The computer 100 may execute analysis algorithmsthat calculate a relative displacement of the patterns on the device 30based on the captured image(s). The computer 100 can be a desktopcomputer, a laptop computer or a tablet computer. In addition, thecomputer 100 and the optical heads 122 can interact using wired links,wireless links, a combination thereof, or any other known or laterdeveloped elements that are capable of supplying and/or communicatingdata to and from the connected computer 100 and the optical heads 122.

Transmission media used as links, for example, can be any suitablecarrier for electrical signals, including coaxial cables, copper wireand fiber optics, and may take the form of acoustic or light waves, suchas those generated during radio-wave and infrared data communications.The computer 100 may communicate directly with the optical heads 122over a network; for example, a Wi-Fi network or other local wirelessnetwork such as Bluetooth. Alternatively, the computer 100 may alsocommunicate with the optical heads 122 indirectly over a network such asInternet. In some embodiments, the computer 100 may include a computerplatform operable to execute applications, which may interact with theoptical heads 122.

The light source 130 is adapted to generate light to illuminate thedevice 30 during performing of the measurement. In FIG. 19 , the lightgenerated by the light source 130 is radiated directly toward the device30, and the light reflected by the device 30 is transmitted to theoptical head 122 right above the device 30. That is, an included angle αbetween an incident light and the reflected light is an acute angle. Insome embodiments, the luminance of the light source 130 may becontrolled by the computer 100.

FIG. 21 is a schematic view of an optical system 10 in accordance withsome embodiments of the present disclosure. Referring to FIG. 21 , theoptical system 10 includes an overlay measuring apparatus 20 and adevice 30. The overlay measuring apparatus 20 is adapted to determinewhether an overlay error exists in the device 30 or not. The overlaymeasuring apparatus 20 includes a computer 100, a stage 110 and animaging assembly 120. The stage 110 and the imaging assembly 120 can becontrolled by the computer 100.

The stage 110, holding the device 30 and capable of horizontal motionand vertical motion, is typically motor driven under control of thecomputer 100. The imaging assembly 120, provided to perform actualmeasurement with the computer 100, can record images of the device 30and generate image information to the computer 100. The computer 100 maydetermine whether the overlay error exists based on the imageinformation. The computer 100 can include a standardized operationsystem capable of running general-purpose application software forassisting with analysis of process performance data and forcommunicating with the stage 110 and imaging assembly 120 viacommunication ports thereof.

The imaging assembly 120 includes a plurality of optical heads 122employed to record one or more images of the device 30, a plurality ofoverlay marks 124 mounted on the optical heads 122, and a light source130 adapted to illuminate the device 30. The overlay marks 124 aremounted on the optical heads 122, are optically transparent, and includetest patterns. In some embodiments, the computer 100 can determinewhether the overlay error exists using only one test pattern.Alternatively, the computer 100 may determine whether the overlay errorexists using the images recorded using different test patterns.

The optical head 122 can receive light projected to the device that isreflected by the device 30 and passes through the respective overlaymark 124. The optical head 122 can further transform the light withpredetermined intensity distribution into corresponding electricalsignals, and the computer 100 can determine whether the overlay errorexists using the electrical signals. In some embodiments, the computer100 executes analysis algorithms that calculate a relative displacementof patterns on the device 30 based on the captured image(s).

The optical head 122 and the light source 130 are disposed on oppositesides of the device 30. More particularly, an incident angle β of thelight emitted from the light source 130 and transmitted to the device 30is equal to a reflected angle δ of the light reflected from the device30 and incident onto one of the optical heads 122.

FIG. 22 is a flow diagram illustrating a method 400 of operating overlaymeasuring apparatus in accordance with some embodiments of the presentdisclosure. Referring to FIGS. 1 and 22 , the method of operatingoverlay measuring apparatus can begin at step S402, in which an imagingassembly 120 is provided. The imaging assembly 120 includes a pluralityof optical heads 122 adapted to record one or more image of a device 30and a plurality of overlay marks 124 mounted on the optical heads 122.

The method then proceeds to a step S404, in which the device 30 to bemeasured is placed on a stage 110. The device 30 includes two or moresuccessive patterned layers. The patterned layers of the device may beformed during front-end-of-line (FEOL) processes or back-end-of-line(BEOL) processes. After the device 30 is set, one of the optical heads122 adapted to capture one or more images is aligned with the device 30(step S406). The optical head 122 and the device 30 may be aligned inaccordance with instructions provided by a computer 100 programmed tocontrol operation of the stage 110 and the optical heads 122. During thealignment, the computer 100 may drive the stage 110 to align the one ofthe optical heads 122. Alternatively, the computer 100 may drive theoptical heads 122 for recording the image to align with the stage 110.

After the optical head 122 and the device 30 are aligned, the opticalhead 122 can start to record the image(s) of the device 30 (step S412).The optical head 122 may transform the recorded images intocorresponding electrical signals and transmit the electrical signals tothe computer 100. The computer 100 can determine whether an overlayerror exists or not, and can determine a relative displacement ofpatterns formed on layers of the device 30 based on the electricalsignals (step S414).

The computer 100 and the optical heads 122 can interact using wiredlinks, wireless links, a combination thereof, or any other known orlater developed elements that are capable of supplying and/orcommunicating data to and from the connected computer 100 and theoptical heads 122. Transmission media used as links, for example, can beany suitable carrier for electrical signals, including coaxial cables,copper wire and fiber optics, and may take a form of acoustic or lightwaves, such as those generated during radio-wave and infrared datacommunications. The computer 100 may communicate directly with theoptical heads 122 over a network; for example, a Wi-Fi network or otherlocal wireless network such as Bluetooth. Alternatively, the computer100 may also communicate with the optical heads 122 indirectly over anetwork such as Internet. In some embodiments, the computer 100 mayinclude a computer platform operable to execute applications, which mayinteract with the optical heads 122.

Material property factors that influence the quality of the imageincluding reflectivity, refractive index, surface roughness, andthickness. Process conditions such as shadowing and light wavelength canalso influence signal quality. Thus, if the measurement is conducted inan environment where background light is insufficient, a light source130 can be optionally provided to illuminate the device 30 before therecording of the device 30 (step S408). Incident light angle mayinfluence image quality; therefore, other optical components, includinga beam splitter 132, may be optionally provided to modify an opticalpath of the light generated by the light source 130, reflected by thedevice 30 and transmitted to the optical head 122 (step 410).Specifically, the beam splitter 132 is positioned at an intersection ofan axis A1 of the light source 130 and an axis A2 of the optical head122 recording the image(s) of the device 30. In some embodiments, thelight generated by the light source 130 is radiated directly toward thedevice 30. In some embodiments, an aperture stop or spatial lightmodulator (not shown) may be provided in the illumination path tocontrol a range of angle of incidence of light on the device 30.

In conclusion, with the configuration of the overlay measuring apparatus20, the test pattern of the overlay mark 124 is mounted on the opticalhead 122 and is replaceable during the measurement; therefore, therecorded image may have a better resolution, and thus the accuracy ofthe measurement is improved.

One aspect of the present disclosure provides an overlay measuringapparatus for determining relative positions of two or more successivepatterned layers of a device. The overlay measuring apparatus comprisesa stage and an optical assembly configured to capture images of thedevice placed on the stage. The optical assembly comprises a pluralityof optical heads for recording images of the device and a plurality ofoverlay marks mounted on the optical heads. The relative positions ofthe two or more successive patterned layers of the device are determinedusing light reflecting off the device and passing through the overlaymark mounted on the respective optical head employed to record theimages of the device.

One aspect of the present disclosure provides an optical system. Theoptical system comprises a device and an overlay measuring apparatus.The device includes a first patterned layer, a second patterned layerabove the first patterned layer, and a first passivation film coveringthe first patterned layer. The overlay measuring apparatus fordetermining relative position of first and second patterned layersincludes a stage and an imaging assembly. The device is placed on thestage. The imaging assembly comprises a plurality of optical heads and aplurality of overlay marks. The plurality of optical heads areconfigured to record at least one image of the device. The plurality ofoverlay marks are assembled on the plurality of optical heads,respectively. The relative position of the first and second patternedlayers are determined using light reflected from the device and passingthrough the respective overlay mark mounted on the optical head.

One aspect of the present disclosure provides a method of operatingoverlay measuring apparatus. The method comprises steps of providing aplurality of optical heads; assembling a plurality of overlay marks onthe plurality of optical heads, respectively; placing a device to bemeasured on a stage; aligning one of the plurality of optical heads withthe device; and recording at least one image of the device.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. For example,many of the processes discussed above can be implemented in differentmethodologies and replaced by other processes, or a combination thereof.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the present disclosure, processes, machines,manufacture, compositions of matter, means, methods or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein, may be utilized according to the presentdisclosure. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods and steps.

What is claimed is:
 1. An overlay measuring apparatus for determiningrelative positions of two or more successive patterned layers of adevice, the overlay measuring apparatus comprising: a computer; a stagewhere the device is placed; and an imaging assembly, comprising: a lightsource configured to generate light to illuminate the device; aplurality of optical heads positioned above the stage and configured torecord at least one image of the device in the computer, wherein thecomputer controls a revolving of each of the optical heads; a pluralityof overlay marks directly and replaceably assembled on the plurality ofoptical heads, respectively, wherein the overlay marks are driven torevolve via the revolving of the optical heads when the optical headsare revolved by the computer, wherein when one of the optical heads isselected to align with the device, the relative positions of thesuccessive patterned layers of the device are determined using lightreflected from the device and passing through the respective overlaymark mounted on the optical head, such that each of the optical headsreceives the light through the respective overlay mark, wherein theoverlay marks are detachably mounted at bottom sides of the opticalheads respectively for measuring an alignment between the successivepatterned layers; and a beam splitter disposed at an intersection ofaxes of the light source and one of the optical heads and between thestage and the overlay mark at the bottom side of one of the opticalheads.
 2. The overlay measuring apparatus of claim 1, wherein thecomputer is configured to execute algorithms that calculate a relativedisplacement of the successive patterned layers using electrical signalstransferred from the image recorded by the optical head, wherein one ofthe optical heads is controlled by the computer for aligning with thedevice to enable the light passing through the corresponding overlaymark at the optical head.
 3. The overlay measuring apparatus of claim 2,wherein the computer analyzes a difference between a predeterminedintensity distribution of light reflected by the device and a uniqueintensity distribution of light reflected by the device and passingthrough the respective overlay mark, in order to obtain the relativedisplacement of the patterned layers on the device.
 4. The overlaymeasuring apparatus of claim 2, wherein the computer is configured tocontrol a movement of the stage to align one of the optical lens withthe device and is configured to select the optical head to record theimage.
 5. The overlay measuring apparatus of claim 1, wherein the lightsource is controlled by the computer to provide the light at selectivewavelengths.
 6. The overlay measuring apparatus of claim 5, wherein thebeam splitter reflects the light generated from the light source, andthe light reflected from the device passes through the beam splitter andthe respective overlay mark and is incident onto the respective opticalhead.
 7. The overlay measuring apparatus of claim 6, further comprising:a first lens between the beam splitter and the device, wherein the lightis reflected by the beam splitter is focused onto the device by thefirst lens; and a second lens between the beam splitter and the overlaymark at the bottom side of one of the optical heads, wherein the lightpassing through the beam splitter is focused onto one of the opticalheads by the second lens.
 8. The overlay measuring apparatus of claim 1,wherein the overlay mark comprises a plurality of micro-structuresarranged in a concentric configuration.
 9. The overlay measuringapparatus of claim 8, wherein the micro-structures include circles. 10.The overlay measuring apparatus of claim 8, wherein the micro-structuresinclude squares.
 11. The overlay measuring apparatus of claim 10,wherein the micro-structures further comprise two lines intersecting ata center of the squares and dividing the squares into quarters.
 12. Theoverlay measuring apparatus of claim 8, wherein the micro-structuresinclude rhombuses.
 13. The overlay measuring apparatus of claim 12,wherein the micro-structures further comprise four lines extendingoutward from centers of sides of an outermost one of the rhombuses. 14.The overlay measuring apparatus of claim 12, wherein themicro-structures further comprise a plurality of lines spaced apart froman outermost one of the rhombuses with a first pitch greater than asecond pitch between two of the rhombuses adjacent to each other. 15.The overlay measuring apparatus of claim 1, wherein the overlay mark iscomposed of repetitious micro-structures.
 16. The overlay measuringapparatus of claim 15, wherein the overlay mark is a rhombus and iscomposed of a plurality of rhomboidal micro-structures.
 17. The overlaymeasuring apparatus of claim 15, wherein the micro-structures arerectangular and are arranged in a running bond configuration.
 18. Theoverlay measuring apparatus of claim 15, wherein the overlay markcomprises rhomboidal or hexagonal micro-structures.
 19. The overlaymeasuring apparatus of claim 15, wherein the micro-structures have agammadion shape.
 20. The overlay measuring apparatus of claim 1, whereinthe overlay mark comprises a plurality of trapezoidal micro-structuresand a plurality of inverted trapezoidal micro-structures alternatelyinterlaced with each other.
 21. The overlay measuring apparatus of claim1, wherein the overlay mark comprises zigzag micro-structures.
 22. Theoverlay measuring apparatus of claim 1, wherein the overlay markcomprises multiple overlapping square micro-structures, and each of theoverlapping square micro-structures is composed of four small squares.